Significance

O-GlcNAc is an abundant, reversible posttranslational modification (PTM) of nuclear and cytoplasmic proteins in animals and plants. O-GlcNAc regulates a wide range of biological processes, and aberrant O-GlcNAcylation is implicated in numerous human diseases. However, key aspects of O-GlcNAc signaling remain poorly understood. For example, it is not known whether “reader” proteins exist to recognize and bind to O-GlcNAc, as is true for many other PTMs. We used a biochemical method to identify candidate human O-GlcNAc reader proteins, and then characterized them at the biochemical and biophysical levels. Our results address a significant gap in the cell signaling field by revealing the biochemical and structural basis for the recognition of O-GlcNAc by conserved human proteins.

Abstract

O-GlcNAc is an intracellular posttranslational modification that governs myriad cell biological processes and is dysregulated in human diseases. Despite this broad pathophysiological significance, the biochemical effects of most O-GlcNAcylation events remain uncharacterized. One prevalent hypothesis is that O-GlcNAc moieties may be recognized by “reader” proteins to effect downstream signaling. However, no general O-GlcNAc readers have been identified, leaving a considerable gap in the field. To elucidate O-GlcNAc signaling mechanisms, we devised a biochemical screen for candidate O-GlcNAc reader proteins. We identified several human proteins, including 14-3-3 isoforms, that bind O-GlcNAc directly and selectively. We demonstrate that 14-3-3 proteins bind O-GlcNAc moieties in human cells, and we present the structures of 14-3-3β/α and γ bound to glycopeptides, providing biophysical insights into O-GlcNAc-mediated protein–protein interactions. Because 14-3-3 proteins also bind to phospho-serine and phospho-threonine, they may integrate information from O-GlcNAc and O-phosphate signaling pathways to regulate numerous physiological functions.

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